Detergents in drainage systems for buildings

Current soil-waste-vent (SWV) system design guides aim to produce ventilate d drainage networks for buildings which protect attached water trap seals f rom unwanted air pressure effects. Such effects may cause trap seal failure that are caused by airflow induction during discharge. The ventilation des ign guides are based on steady-state experiments utilising cold clean water as a test media. However, most 'grey' and 'black' water sources are dosed with detergent, and are often warm, which significantly alters the behaviou r when compared to clean water. Thus, current design standards provide only approximations of SWV system response. Results indicate that induced airfl ows in warm detergent-dosed water can be significantly higher than those me asured in clean water systems, by a factor of more than 2. This paper quant ifies the effect of detergents in SWV systems in terms of observed air entr ainment rates and previously published research on the factors that contrib ute to air entrainment. Results of previous work are cast into dimensionles s groupings suitable for inclusion into a mathematical simulation model bas ed on a finite difference scheme. It utilises the method of characteristics as a solution technique to simulate drainage system operation via the equa tions that define unsteady partially filled or full bore pipe flows and the boundary conditions represented by water traps and other common system com ponents. (C) 2001 Elsevier Science Ltd. All rights reserved.